In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during the transfer step, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or van der Waals forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner and debris (hereinafter commonly referred to in common as "toner") remaining on the surface be cleaned thoroughly therefrom.
Numerous cleaning methods have been proposed to accomplish effective toner release from the imaging surface, including blades supported in doctoring or wiping modes, rotating or sweeping neutral or electrically-biased fiber brushes, magnetic brushes, vacuum systems and various combinations thereof. However, toner components and debris are tightly adhered to the surface by electrostatic and mechanical forces, and tend to resist release. Accordingly, particularly when the shape of a particle is not optimum, e.g. a flat toner particle, prior cleaning methods do not achieve optimum cleaning operation. Additionally, it has been noted that even when pre-clean charging, the charge at the toner and photoreceptor surface interface is not neutralized to the extent desirable for subsequent toner release. This problem is believed to arise from the failure of neutralizing ions from the pre-clean charging device to reach all the charged areas on the toner and photoreceptor. Even when precleaning illumination is provided, to dissipate charge on the surface, by flooding the back side of a translucent photoreceptor, tightly bound charge remains at the particle/imaging surface interface.
U.S. Pat. No. 4,111,546 to Maret proposes enhancing cleaning by applying high frequency vibratory energy to an imaging surface with a vibratory member, coupled to an imaging surface at the cleaning station to obtain toner release. The vibratory member described is a horn arrangement excited with a piezoelectric transducer (PZT element) at a frequency in the range of about 20 kilohertz. However, such an arrangement is rather noisy, and requires a relatively high power supply to obtain optimum vibration. U.S. Pat. No. 4,684,242 to Schultz describes a cleaning apparatus that provides a magnetically permeable cleaning fluid held within a cleaning chamber, wherein an ultrasonic horn driven by piezoelectric element is coupled to the backside of the imaging surface to vibrate the fluid within the chamber for enhanced cleaning. U.S. Pat. No. 4,007,982 to Stange provides a cleaning blade with an edge vibrated at a frequency to substantially reduce the frictional resistance between the blade edge and the imaging surface, preferably at ultrasonic frequencies. U.S. Pat. No. 4,121,947 to Hemphill provides an arrangement which vibrates a photoreceptor to dislodge toner particles by entraining the photoreceptor about a roller, while rotating the roller about an eccentric axis. Xerox Disclosure Journal "Floating Diaphragm Vacuum Shoe, by Hull et al., Vol. 2, No. 6, November/December 1977 shows a vacuum cleaning shoe wherein a diaphragm is oscillated in the ultrasonic range. U.S. Pat. No. 3,653,758 to Trimmer et al., suggests that transfer of toner from an imaging surface to a substrate may be enhanced by applying vibratory energy to the backside of an imaging surface at the transfer station. U.S. Pat. No. 4,833,503 to Snelling discloses the use of a PZT device for the enhancement of development in a color printing system.